This very simple experiment demonstrates in an elegant way the particle nature of the photons that make up light.
What is needed:
1) A metal plate with a small hole in it. Preferably one made of steel. The size isn’t
all that important, but generally bigger is better. (Up to a reasonable size of
course.)
2) A thin wire to hang the plate up.
3) A
photoflash. Any flash on an ordinary camera will do, but again bigger is
better.
What to do:
1) Hang the metal plate up so it swings freely.
2)
Place the flash a few cm from the plate and set it
off
3)
If you listen carefully you will hear a faint
“ping” from the plate
Why?
The photons making up the flashlight transfer their momentum to the metal atoms.
This in turn
sets the atoms oscillating which in turn we detect as sound.